Delay communication system



A 6, 1947. L. KATCHATQUROFF A 1 2,426,223

DELAY COMMUNICATION SYSTEM Filed April 13, 1943 3 Sheets-Sheet g g INVENTOR.

LEON mru-mraueop;

if i

Aug. 26, 1947. L. KATCHATOUROFF 2,426,223

DELAY COMMUNICATION SYSTEM Filed April 13, 1943 3 Sheets-Sheet 2 F TI TIA I IN VEN TOR. LEO/Y KHTCHHTOUROFF Aug; 26, 1947. L. KATCHATOUROFF 2,426,223

DELAY COMMUNICATION SYSTEM Filed April 15, 1945 m 5 Sheets-Sheet 5 INVENTOR. LEON KHTCHHT PO Patented Aug. 26, 1947 DELAY COMMUNICATION SYSTEM Leon Katchatouroff, Paris 7, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 13, 1943, Serial No. 482,904 In France January 31, 19 11 This invention is concerned with electrical telecommunication systems capable of simultaneous transmission of telephone conversations and telegraph communications at voice frequency by means of teleprinters.

In systems. of this kind it is advisable to utilize a conventional two-wire telephone line for both directions of transmission without the necessity of effecting a switching operation in order to communicate simultaneously by telephone and by telegraph in either direction.

One of the objects of this invention is to provide a system of this type which will permit operation of the devices usually provided in teleprinting systems for the local control recording of the transmitted messages simultaneously with operation of the telephone apparatus and teleprinter transmitting apparatus.

In systems of this nature the control devices generally consist of a local teleprinter receiver to which the teleprinter signals are applied at the time of their transmission over the connecting or trunk line.

The telephone and teleprinter units are respectively connected to a common transmission line by suitable filters. However, during the operation of such a system the impedance at the terminals of the narrow band filter of the teleprinter system which faces or is connected to the line varies abruptly within the band of frequencies used for telegraphy. This variation so unbalances the relation between the impedance facing the line and the impedance of the attenuation circuit used to transmit the signals to the local printing recorder that operation of this recorder becomes erratic, if not impossible, due to the distortion of the signals.

An object of this invention is to provide a system in which simultaneous communications of this kind with operation of a local printer may be effected while preventing the improper operation of the printer due to the effect of the variation of the line impedance on the local transmission circuits to the printer.

According to one feature of the invention a unipolar switching device mechanically actuated by the teleprinter is inserted in the local control circuit in such a way that during the period of transmission of the telegraph signals it connects an impedance in the circuit to the local printer which provides the best value of signal level at the input terminals thereof. Furthermore, the transmitter circuits are considerably unbalanced'in order to prevent variation of the line impedance from causing variation. of the 6 Claims. (01. 179 4) local reception signal level with the various frequency components.

Other objects of this invention will be apparent from the following detailed description of one embodiment thereof.

This invention resides substantially in the combination, construction, arrangement and relative location of parts, all as will be described in detail below.

In the accompanying drawings,

Figure 1 is a schematic illustration of the conventional arrangement of a teleprinter system;

Figure 2 is a schematic illustration of the arrangement of a system for the simultaneous transmission of telephone and telegraph signals and the reception thereof;

Figure 3 diagrammatically illustrates the manner of operation of the unipolar switching device employed in the combination of this invention; and

Figure 4 is a schematic illustration of one embodiment of the invention herein disclosed for the simultaneous transmission of telephone and telegraph signals and the reception thereof incorporating the features of this invention.

Referring first to Figure 1, there is shown schematically one example of an arrangement of circuits for the transmission of telegraph signals at voice frequencies between the two stations A and B. These two stations are shown connected by a two-wire telephone line L. Each transmitter includes an oscillator 0A and OB which feeds through differential transformers TDA and TDB respectively the line Lfor the purpose of transmitting over it the signals produced through actuation of either of the teleprinter contacts KA and KB which opens and closes in cadence with the telegraph signals so that the oscillators 0A or OB apply to the line a voice frequency current that is interrupted and restored at the same cadence. The local control printers comprise driving relays RA and RB and the associated equipment RLA and RLB respectively, also fed by the oscillators.

The differential secondaries of the transformers TDA and 'IDB have connected thereto the variable impedance PA and PB respectively, which are adjustable to have a slightly different impedance from the impedance Z that faces the terminals of the line L. During transmission about one-half of the signal energy is accordingly dissipated in the line L, a very small fraction being transmitted to RLA or RLB, depending upon which station is transmitting, and the rest being dissipated in the corresponding impedance PA or PB. The corresponding driving relay at the other end of the line BA or RB is actuated and effects the printing of the corresponding characters. Since the transformers TDA and TDB are unbalanced by a desired slight amount, a fraction of the energy from the corresponding oscillator A or OB through the transformer is directed to the apparatus RLA or RLB to cause the operation of the corresponding relay RA or RB at the same time as the remote relay with respect to the one in operation, that is the one at the far end of the line, is operated. The teleprinter of station A, for example, accordingly prints the same characters as the teleprinter of station B, and this constitutes local control recording. The op eration, of course, would be reversed for transmission from station B to station A.

The frequency band width required for a current transmission of the 50 baud telegraph signals is about 300 cycles for a system without intermediate relays. Indeed, in a system of this kind it is desirable to give the signals a substantially rectangular shape. So long as only a telegraph communication is transmitted over the two-wire line no narrow band filter is placed at the terminals of the line. The impedance Z has substantially the same value for all the components in the above mentioned 300 cycle band. Since the resistance of the impedance PA or PB is adjusted the unbalance obtained between it and the impedance A has likewise the same value for all the components and as a result of this the signals transmitted through the differential transformer TDA or TDB to the local receiver are reduced to the proper level and are not dissipated since the attenuation for all of the signal components is uniform and the local circuit therefore operates properly.

For the simultaneous transmission of a telephone signal and a telegraph signal over the line L, it is preferable to use a circuit like the one shown schematically in Figure 2. The teleprinter instruments are shown at TIA and TIB, and the telephone apparatus at TPA and TPB. The telephone equipment may be of any known suitable type and the teleprinter instruments and associated circuits may be like those disclosed in Figure 1. Narrow band telegraph filters FIA and FIB and telephone filters FPA and FPB are provided at each station for the purpose of providing two separate channels. Of course, the construction of these filters need not be explained in detail since they are all well known in these arts.

With a circuit of this kind, however, it will be impossible to operate the local control printers satisfactorily for the recording of the telegraph transmission. Indeed, the impedance Z that faces the terminals of the line is in this case the input impedance of the narrow band filters FIA or FIB. This impedance varies abruptly in the 300 cycle band used for telegraphy. The amount of the unbalance between the impedance PA or PB and the impedance Z would vary enormously according to the frequency of the signal component in question. As a result of this the signals transmitted through the transformer TD to the local receiver would be completely distorted. Local control recording would consequently become impossible.

According to features of this invention a circuit of this kind may be satisfactorily used by providing a unipolar change-over switch that is actuated mechanically by the teleprinter. One mode of operation of such a device is illustrated in Figure 3 in connection with an em od m of such a change-over switch which is identical with the transmission reception switch of known teleprinter apparatus employing direct current transmission. The insertion of such a device in the circuit of Figure 2 is illustrated in Figure 4, including a modification to provide the subject matter of this invention.

At the left side of Figure 3 are shown the two contacts K1 and K2 of the sending telegraph switch (KA or KB, Figure 1) and of this unipolar change-over switch, respectively, as well as the teleprinters driving motor M which actuates the two contacts, as indicated by the dotted line connection. The arrangement of each of these contacts is such that the current in relation to time through the contacts for each signal is shown in the graphs C and D aligned respectively with the contacts K1 and K2.

When a character key of the teleprinter is depressed the switch K1 effects a series of circuit interruptions represented by curve C which results in the transmission of the corresponding telegraph signal. In the system selected as an example a character code is represented by five working or marking and resting or spacing intervals of 20 milliseconds each preceded and followed by starting and stopping signals of 20 and 30 milliseconds respectively, for the positioning and return to rest of the type wheel of the receiver. At the same time and in synchronism the switch K2 is mechanically opened to open its working contact for the duration and transmission of the character as represented by the curve D. The resistance of the impedance P (Figure 4) has a value very different from the impedance Z. If for example Z fluctuates around a value of 800 ohms in the telegraph band the value of P will be about 400 ohms. When the key corresponding to a particular character is depressed the energy transmitted by the oscillator O is divided between the line L and the resistance P. A considerable voltage is also applied to the input terminals G, H of the local receiver RL. However. contact K2 of the unipolar change-over switch opens for the entire time of transmission of the character signal, thereby connecting the resistance Q in the input circuit of the local receiver. The signal level actually applied to the receiver is thus reduced to a predetermined value. Since the transformer TD is completely unbalanced the variations of the impedance Z within the telegraph band do not influence the level of the signal components at the terminals G, H. The signal is transmitted to and the desired local control of the receiver is obtained without distortion.

As soon as the character is transmitted contact K2 closes and the receiver recovers its sensitivity and is ready to receive a weak signal coming over the line from the distant station. A system of this kind normally permits the use of a two-Wire telephone line for the simultaneous transmission of a bi-lateral telephone communication independent of telegraph signals and a bi-lateral telegraph communication with local recording of the transmitted telephone messages. The telegraph connection does not require any other relay than the driving relays of the two connecting stations, and as a source of current only the network or other available high voltage supply.

From the above description it is evident that the single embodiment of this invention as disclosed herein does not comprise the only embodiment thereof which will suggest itself to those skilled in the art. I do not therefore desire to be strictly limited to the disclosure as given for purposes of illustration, but rather to the scope of the appended claims.

What is claimed is:

1. In a signal system the combination including a transmission line, telephone transmitting and receiving apparatus coupled to the respective ends of the line through filters, a telegraph carrier current generator, means for controlling said current to impart telegraph signal characteristics thereto of a narrow low frequency band, a differential transformer primary fed by said generator, a narrow band filter connecting the secondary of the transformer to said line, a local telegraph printer having an input circuit connected to the secondary of said transformer, and means for connecting an impedance in said input circuit during the periods of telegraph signal transmission originating at the station where said local telegraph printer is located, while maintaining said telephone transmitting and receiving apparatus coupled to said line.

2. The combination recited in claim 1, in which said last means includes a resistance in said inputcircuit, a switch normally short-cir-- cuiting said resistance, and means for opening said switch during periods of telegraph signal transmission.

3. The combination recited in claim 1, in which the secondary of said transformer comprises two portions, one portion being connected to the input of the narrow band filter and to the input of said local printer, and the other portion being connected to the input of said printer, said second portion including a variable resistance.

4. The combination recited in claim 1, in which the secondary of said transformer comprises two portions, one portion being connected to the input of the narrow band filter and to the input of said local printer, and the other portion being connected to the input of said printer,

said second portion being difierentially wound with respect to said first portion.

5. The combination recited in claim 1, in which the secondary of said transformer comprises two portions, one portion being connected to the input of the narrow band filter and to the input of said local printer, the other portion being connected to the input of said printer and said last means comprising a normally shortcircuited resistance in said input circuit, and means for opening the short circuit during periods of telegraph signal transmission originating at the station where said local telegraph printer is located, while maintaining said telephone transmitting and receiving apparatus coupled to said line.

6. The combination recited in claim 1, in which the secondary of said transformer comprises two portions, one portion being connected to the input of the narrow band filter and to the input of said local printer, the other portion being connected to the'input of said printer, said second portion being diiferentially wound with respect to said first portion and said last means comprising a normally short-circuited resistance in said input circuit and means for opening the short circuit during periods -of telegraph signal transmission originating at the station Where said local telegraph printer is located, while maintaining said telephone transmitting and receiving apparatus coupled to said line.

L. KATCI-IATOUROFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,121 Hagen Dec. 22, 1942 2,254,342 Zenner Sept. 2, 1941 2,106,352 Kinkead Jan. 25, 1938 1,621,557 Nyquist Mar. 22, 192" 

